code: def test_3d_error():
      f = np.zeros((32, 16, 3))
      with pytest.raises(ValueError):
          sobel(f)
  
file_path: mahotas/mahotas/tests/test_edge.py
imports: from mahotas.edge import sobel
  import pytest
  import mahotas
  import numpy
label_desc: Use image node_id 6 for calling a global function with example usage: test_3d_error() without return types